Study of cross-conjugated iso-polytriacetylenes and related oligoenynes

Two series of monodisperse cross-conjugated oligomers based on enyne repeat units have been realized. The first class of molecules, iso-polytriacetylenes (iso-PTAs, 2), was divergently synthesized using an iterative sequence of palladium-catalyzed cross-coupling reactions of vinyl triflate 5 with terminal alkynes. The second series of oligoenynes (17-20) are based on an octatetrayne backbone, and result from homocoupling of the differentially protected iso-PTA oligomers 8-11. The longest member of this series, 20, spans ca. 5.6 nm from Si atom to Si atom and is composed of a contiguous sequence of 44 sp and sp(2) carbons. The lowest energy electronic absorption band for iso-PTA dimers in the progression 13 --> 9 --> 16 is consistently red-shifted as a result of extending the cross-conjugated structure. A similar comparison within each series (i.e., 16, 6-7, or 17-20), however, suggests little effect on the electronic characteristics of these molecules as oligomer length is increased. The solid-state properties of one derivative, 17, are also described.     

Theoretical approach and the practice to the evaluation of structural parameters characterizing concentration polarization alongside ion-exchange membranes by means of dielectric measurement

As the application of a dielectric theory proposed previously (J Membrane Sci 64:153–161 (1991)), theoretical formulation and the practical procedure of dielectric analysis are developed to calculate the structural parameters such as the conductivity gradient and the thickness of the concentration polarization layer, the capacitances and the conductances of the two adjoining aqueous phases from the observed dielectric parameters. The procedure of calculation consequent upon the theoretical formulation was applied to double relaxation data observed for cation-exchange membrane systems under application of d.c. bias voltage. As a consequence, the structural parameters of concentration polarization were readily obtained with accuracy.     

The uranium-Xylidyl Blue I complex and its application in linear sweep polarography

The linear sweep polarographic wave of the uranium-Xylidyl Blue I complex in ethylenediamine-1,10-phenanthroline-hydrochloric acid medium has been studied. The complex, corresponding to UO(2)(XBI)(2-)(2) with log beta' = 9.09 (by polarography), 8.81 (by spectrophotometry), is strongly adsorbed on the surface of the mercury electrode. The polarographic wave is attributed to the reduction of Xylidyl Blue I in the complex. The method is very sensitive with a detection limit of 3 x 10(-8)M. The wave height is proportional to the concentration of uranium over the range 8 x 10(-8)-7 x 10(-6)M. Solvent extraction is used to separate possible interferences. The recommended procedure has been applied to the determination of trace amounts of uranium in ores.     

Noble gas-transition metal complexes: coordination of ScO+ by multiple Ar, Kr, and Xe atoms in noble gas matrixes

The combination of matrix isolation infrared spectroscopic and density functional calculation results provides strong evidence that the transition metal monoxide cation, ScO+, coordinates five noble gas atoms in forming the [ScO(Ng)5]+ (Ng = Ar, Kr, or Xe) complexes in noble gas matrixes.     

Synthesis of substituted carbazoles by a vinylic to aryl palladium migration involving domino C-H activation processes

Substituted carbazoles are readily prepared in good yields by the palladium-catalyzed cross-coupling of alkynes and N-(3-iodophenyl)anilines. This process proceeds by carbopalladation of the alkyne, heteroatom-directed vinylic to aryl palladium migration, and ring closure involving two consecutive C-H activation processes. The process has also been expanded to the synthesis of an indole. [Structure: see text]     

Rheological properties of the aqueous mixtures of cationic-anionic surfactants

The rheological properties of the aqueous mixtures of cationic-anionic surfactants, both in single-phase systems and in aqueous two-phase systems, have been studied. Bizarre rheological properties —negative thixotropy, viscoelasticity and hihg viscosity of shear rate dependent at relatively low concentration — have been observed. An unusual viscosity change, that is, viscosity lowering with increasing concentration, was obtained. The negative thixotropy might be due to the existence of lamellar or sheet-like micelles, viscoelasticity might be induced by rodlike and lamellar or sheet-like micelles, the high viscosity might be a consequence of the formation of network by long rodlike micelles and the concentration-induced viscosity lowering could be interpreted in terms of the decrease of micellar dimensions with concentration.     

Trypsin activity assay in substrate-specific one- and two-dimensional gels: a powerful method to separate and characterize novel proteases in active form in biological samples

To separate and identify the proteases, a substrate-specific, sensitive assay in sodium dodecyl sulfate (SDS)-polyacrylamide gels after two-dimensional (2-D) electrophoresis has been developed. This method allows simultaneous determination of protease cleavage specificity, molecular weight, isoelectric point, and if necessary, amino acid sequencing. After isoelectric focusing in immobilized pH gradient (IPG) strips (pH 6-11) (first dimension), trypsin was electrophoresed in 12% SDS polyacrylamide gels (second dimension) copolymerized with Boc-Gln-Ala-Arg-MCA (4-methyl-coumaryl-7-amide). The gels were washed in cold 2.5% Triton X-100 and water, and incubated in assay buffer (6.3 mM Bicine, 100 mM NaCl). Trypsin cleavage of the peptide-MCA generated fluorescent 7-amino-4-methyl-coumarin. In 1-D gels, as low as 500 pg trypsin could be detected and trypsin band volumes correlated linearly with the amounts of trypsin (R(2) = 0.999). In 2-D gels, the lowest amount of trypsin detected was 1 ng. The linear regression of spot volume and loading amount was still good (R(2) = 0.974). To optimize renaturation conditions, 5x5 min washes with 2.5% Triton X-100 and water, respectively, gave the strongest band volume. For fluorescence development, an assay buffer at pH 9 was the best; incubation at 37 degrees C for 30 min was sufficient. The method has application for identifying novel proteases as it does not rely on antibodies.